Electric motor for watches

ABSTRACT

An electric motor for watches, composed of a rotor with permanent magnetization, a stator winding without core and with even spirals which presents a symmetrical plane parallel to the spirals and containing the axle of the rotor, a winding support made of non-magnetic material and an annular yoke made of a ferromagnetic material with high permeability and low remanence surrounding the support.

United States Patent [1 1 Vuffray 11] 3,747,320 July 24, 1973 ELECTRICMOTOR, FOR WATCHES [75] Inventor: Georges C. Vuifray, La

ChauX-de-Fonds, Switzerland [73] Assignee: Girard-Perregaux S.A., La

Chaux-de-Fonds, Neuchatel, Switzerland [22] Filed: Jan. 5, 1972 211Appl. No.: 215,573

Related US. Application Data [62] Division of Ser. No. 79,753, Oct. 12,1970, Pat. No. 3,652,884.

[30] Foreign Application Priority Data Oct; 13, 1969 Switzerland15381/69 Apr. 10, 1970 Switzerland...-. 5353/70 [52] 0.8. Cl. 58/23 D,310/156 [51] Int. Cl. .J, G04!) l/00 [58] Field of Search... 310/156,194, 257,

310/43, 42, 46, 254, 258, 259, 152, 179; 58/23 D, 23 R, 26 A, 41 B i[56] References Cited UNITED STATES PATENTS 2,499,326 2/1950 2,988,8686/1961 3,375,423 3/1968 3,383,534 5/1968v 3,652,884 3/1972 Vuffray310/257 X Primary Examiner-Richard B. Wilkinson Assistant Examiner-U.Weldon Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT Anelectric motor for watches, composed of a rotor with permanentmagnetization, a stator winding without core and with even spirals whichpresents a symmetrical plane parallel to the spirals and containing theaxle of the rotor, a winding support made of nonmagnetic material and anannular yoke made of a ferromagnetic material with high permeability andlow remanence surrounding the support.

12 Claims, 7 Drawing Figures PATENIED JUL 2 4 I975 SHEET 1 BF 4 FIG.I

PAIENIEB JUL 2 4 5975 FIG.

sum 2 er 4 PATENTED JUL24|975 v 3. 747. 3 20 sum 3 or 4 FIG.5

ELECTRIC MOTOR FOR WATCHES This application is a division of co-pendingU. S. No. application Ser. No. 79,753, now U.S. Pat. nno. 3,652,884,issued Mar. 28, 1972.

' The purpose of the invention is to provide a motor of minimum sizewith the highest possible degree of efficiency and which is capable ofoperating under the effect of surges of current sentinto the statorwinding.

To achieve this purpose, the motor in accordance with the invention ischaracterized by the fact that said yoke has at least one pair ofopenings diametrically opposed made in an annular area which extends tothe level of the rotor, the central axis of these openings being obliquewith respect to the magnetic axis of the winding.

A particular form of design of this motor can be used to drive the handsof a small quartz clock. The motor comprises a unit generallycylindrical in appearance which can be designed in a manner completelyindependent of the other elements of the watch and is intended for beingattached to an appropriate place in the frame of the watch. In this formof design the bearings are connected to two support elements of a roundshape assembled coaxially one against the other and adjusted withrespect to one another by means of a cylindrical yoke made offerromagnetic material. However, in certain preferred forms of designthe motor according to the invention is supposed to be housed inside ofthe movement of an electronic wrist watch, for example a wrist watch ofquartz crystal.

It is known that in order to achieve this purpose it is necessary notonly to reduce the size of the motor but also to prevent any mechanicalloss since the power source is composed of one or just a few miniaturebatteries and it is important to reduce power consumption in order toassure long life of the batteries. It is therefore necessary that therebe a high degree of mechanical efficiency, in other words that the lossthrough rubessential that the distances between the axes of the variouswatch-train elements be held at the smallest possiblektolerances.v

In such forms of design the bearings of the rotor are interlocked withtwo elements of the frame connected to one another and the windingsupport is held in place between said frame elements by appropriatecentering elements offered by the frame elements and the windingsupport. I I

The attached sketch shows, by way Of example, several forms of design ofthe motor according to the invention.

FIG. 1 is a sectional view of a first embodiment according to a planeperpendicular to'the magnetic axis of the stator winding;

FIG. 2 is an overhead view;

FIG. 3 is a section view according to a plane containing the magneticaxis of the stator winding;

FIG. 4 is a blown-up view of the three pieces comprising the body of themotor;

FIG 5 is a sectional view of the second embodiment;

FIG. 6 is a cut-away view from overhead of this second embodiment; and

FIG. 7 is a drawing in perspective of a design variation of the windingsupport.

The rotor 1 of the motor in FIG. 1 is a cylindrical piece made offerromagnetic material with a high degree of remanence magnetizedaccording to a diametrical plane. This piece is mounted on a shaft 2which has at its lower extremity, in FIG. 1, a pivot 3 inserted into abearing 4 comprised of a clockwork stone and at its upper extremity anextended pivot which passes through a second bearing 6 formed as is thebearing 4. The pivot 5 extends to the outside of the motor where itaccepts a pinion or other driving mechanism.

The bearings 4 and are connected with the body of the motor which itselfis composed of three pieces, a seating 7, a lid 8 and a yoke, or sleeve,9. They can be of a plastic material and formed by injection with thebearings, in which case the stones 4 and 6 are done away with or are ofa non-magnetic metal. In the latter case they can be made by machining.The seating 7 is a piece of a generally cylindrical shape which has inits upper front side a cylindrical housing 10 the bottom of which ispierced by a central opening 11. In its lower side and in its externalside there are groves 12 and 12a (FIG. 4) which are parallel andarranged symmetrically on both sides of a diametrical plane. Betweenthese grooves there are two diametrically-opposed web elements 13 and130. Furthermore, the remaining part of the external side has shoulders14 and 14a and elements of cylindrical spans 15 and 15a. The lid 8 has asimilar structure, with the exception of the fact that in place of theshoulders 14, 14a and the lateral spans 15 and 15a there arediametrically-opposed protruding elements 16 and 16a presenting concaveinside surfaces 17 adjusted to the spans 15 and 1511 so as to permit thefitting of the lid 8 Onto the seating 7 in a position which is coaxialwith respect to the latter. The cylindrical housing 21 (FIG. 3) providedin the lower surface of the piece 8 forms with the housing 10 acylindrical chamber the dimensions of which are slightly larger thanthose of the rotor 1 and which is intended for holding it, the centralopening 11 of the piece 7 and the corresponding opening of the piece 8being equipped, each one of them, with one of the bearings 4 and6. Whenthe two pieces 7 and 8 are assembled the grooves 12 and 12a, as well asthe corresponding grooves 18 and 18a of the piece 8, form continuouspassages of an annular shape in which the two parallel bodies 23 and 24of the stator winding are wound. The spirals of this winding are thuscontained in parallel planes perpendicular to the magnetic axis of thewinding. The entire winding presents, furthermore, a diametricalsymmetrical plane parallel to the plane of the spirals and extend ing inthe direction of the webs 13, 13a of the seating .7 and in the directionof the corresponding webs 19,

19a of the lid 8.

It can be seen from FIG. 2 that the inside extremities of the webs 13and 13a are cut in bezel according to the lines 25 and 26. Thisarrangement provides between the two grooves of the body of the motor apassageway for the winding wire during the subsequent winding of the twobodies of coils.

The yoke, or sleeve, 9 is made of ferromagnetic material of lowremanence and high permeability. It can be of Armco iron and produced bymachining, moulding, laminating or else by calcing. It is of acylindrical tubular shape and its inside surface is adjusted to theoutside diameter of the pieces 7 and 8. This ring serves to close themagnetic circuit of the motor and protect it from the external fields towhich it might be subjected.

In order to facilitate the mounting it is possible, for example, toimpart to the outside surface a slightly conical shape and to adjust theinside surface with a slightly more marked tightening in the upper partthan in the lower part. The ring 9 can thus be expelled easily onto thebody shaped by the junction of the pieces 7 and 8. However, as will beseen further on, it is also possible to adjust the ring 9 so that itrotates freely on the body of the motor.

The sleeve 9 has two diametrically-opposed openings 28 and 29 each oneof which extends in length onto an arc of a circle of approximately 120.Their width is equal to about one third of the total height of the ring,that is to say one third of the height of the motor and, as can be seenfrom FIG. 3, this width of the openings 28 and 29 is approximately equalto the axial length of the rotor l. The two extremities of each openingare rounded out in a semicircle while the central parts of the edges ofthe openings extend in planes perpendicular to the axis of the rotor. Indriving the ring 9 onto the body of the motor it is oriented so that oneof the ex tremities of each opening falls into the axis defined by thewebs 13, 13a, 19, 19a resulting in the other extremity of the openingsbeing oriented to about 30 respect to the magnetic axis of the windingwhile the central axis of the full parts existing between the openingsis oriented by 60 with respect to the magnetic axis. In other forms ofdesign the length of the openings could be different. It could bereduced to approximately 60. It was found, however, that optimumefficiency is obtained with the dimensions indicated above.

The motor which has been described is meant to be controlled by surgesof current and to turn step by step. In the absence of current themagnetic axis of the rotor shifts spontaneously into a directionperpendicular to the central axis of the openings 28 and 29. It is, ineffect, in this position that the magnetic circuit passing through therotor and the sleeve 9 is the shortest. With the arrangement representedin FIG. 2 and with the motor stopped in the preferred position definedabove, if a surge of current is sent into the stator winding such thatit imparts a torque on the rotor making it turn in the direction of thehands of the watch this current surge will drive the rotor to the pointwhere its magnetic axis is parallel to the magnetic axis of the winding.After the surge of current has stopped, the torque of magnetic recoilonto the rotor will make it turn to a position which is diametricallyopposed to that which it had in the beginning. If the second surge whichis sent into the stator winding is of the opposite polarity of that ofthe first surge then the rotor will effect a second halfturn in the samedirection as the first one. The sending of surges of current ofalternate polarity at regular intervals of time into the stator windingtherefore causes an irregular movement of rotation of 180 by the rotor1.

Although this form of operation of the motor is a particularlyadvantageous one, it is obvious that the rotor described can also bedriven in continuous rotation. To do this the surges of current must besufficiently close in order to prevent any stoppage in the restpositions determined by the openings of the ring 9. Furthermore, themovement can also be an oscillating movement. This will be the case ifthe surges of current sent into the stator winding are of the samepolarity. The rotor will oscillate between the direction defined by thecentral axis of the full parts of the rings and the magnetic axis of thewinding. It is to be noted in particular that such an oscillation canoccur in the case of the operation first described if the polarity ofthe surge of current sent into the stator winding is such that thetorque experienced by the rotor tends to make it turn in the oppositedirection of the hands of the watch. The rotor will rotate a maximum of30 in this direction and then will return to its initial position andthe next surge of current will drive it into the desired direction. Itis also seen that it suffices to make the ring 9 turn by an angle of 60with respect to the body of the motor in the op posite direction of thehands of the watch in order for the motor to turn in the oppositedirection under the same conditions as above.

The moving part mounted on the extremity of the shaft 2 can be a piniondriving a clockwork which itself comprises moving parts for seconds,minutes and hours carrying the corresponding indicator hands into anelectronic watch, for example a quartz watch or small clock. Thefrequency of the surges can be, for example, one second, the motor thenturning by jerks at a speed of 30 revolutions per minute.

In another form of design it is also possible to mount on the pivot 5 anelement carrying a catch working to gether with a ratchet-wheel so as todrive it in step-bystep rotation.

The motor represented in FIGS. 5 and 6 is incorporated in the movementof a wrist watch containing a quartz crystal as the essential element ofits time cycle base. The power source composed of one or two miniaturebatteries providing a voltage of 1.2 volt maintains the oscillations ofthe time cycle and feeds a frequency divider whose output suppliessurges of alternating polarity at a frequency of 0.5 Hz. These surgesdrive the stator winding of the motor and make it turn at a mean rate ofrotation of 30 revolutions per minute by steps of 180. In its turn thismotor drives a speedreducing gear train which activates the hands of thewatch. All of the elements of the movement are housed between a mountingplate 31 and one or more bridges including, among others, a-clockworkbridge 32. Some of these ele'ments'can also be arranged on the outsidesurfaces of the mounting plate or of the bridges. At the site of themotor the mounting plate has an opening 33 into which a stone 34 isdriven which forms the bearing in which the pivot 35 of the shaft 36turns. On both sides of this opening the mounting plate has two morerectangular openings 37 and 38 the purpose of which shall be describedfurther on.

The bridge 32 is attached to the mounting plate 31 by the conventionalmeans such as guides or a screw, for example. It has a round'opening 39coaxial to the opening 33 and into which there is driven a stoneconstituting the other bearing of the shaft 36. On both sides of thisopening 39 there are pierced two rectangular openings 41 and 42 whichcorrespond to the openings 37 and 38, respectively. The stone 39 ispassed through by a pivot 43 offered by the shaft 36 at its extremity onthe bridge side and this pivot, of a length greater than that of pivot35, protrudes at the outside of the bridge 32 so as to accept a pinion(not shown). This pinion can be driven onto the tipof the shaft 43 afterthe mounting of the movement, as shall be seen later on.

The rotor has a permanent magnet 44 cylindrical in shape which is drivenonto the central part of the shaft 36. The latter is made of steel,while the permanent magnet is made of a material with a strong coercivefield and a high maximum 8H, for example anisotropic ferrite,platinum-cobalt alloy, samarium-cobalt alloy, or another magneticmaterial of high performance. The permanent magnet of the rotor ismagnetized diametrically.

The winding support is formed by two coil elements 45 and 46 similar inshape and arranged symmetrically on both sides of the rotor. As can beseen in FIG. 5, each one of these coil elements comprises a solid part,the height of which corresponds to the distance between the mountingplate 31 and the bridge 32, and a protruding part which extends oppositeto the permanent magnet 44, which is somewhat higher than the axiallength of this part of the rotor and which surrounds it partially. Eachcoil support 45, 46 presents opposite the cylindrical surface of therotor a surface 47 which constitutes a portion of a cylindrical surfacecoaxial to the rotor. The protruding part of the coil elements serve asa support for each one of the coils 48, 49. The latter are woundseparately onto each coil element in the form of even spirals. Lastly,in thecase represented, each coil has a rectangular section. Preferablythe coil elements 45 and 46 will be made of an injected plasticmaterial, for example plexiglas, polyvinylchloride, teflon, materialwith a glass fiber base, ceramic material, etc. The shape of these coilsis relatively simple and they can thus also be obtained by machining.Each coil element has, in the upper surface and in the lower surface,two recessed holes into which fixing bases 50 are driven which serve forpositioning the coil supports at the time of the mounting.

Lastly, the motor comprises a yoke, or sleeve, 51 composed of a piece oftubular shape made of a ferromagnetic material of high permeability andlow remanence which surrounds the coil elements 45 and 46. This ring isplaced into a round groove 52 cut in the inside surface of the mountingplate. As in the first form of design, it has openings53 intended forassuring the orientation of the rotor in the absence of a surge ofcurrentin the stator coils.

The different elements of the motor can be manufactured independently ofone another. To mount the motor onto the mounting plate 31 it sufficesto take the two coil elements 45 and 46, fit them onto the permanentmagnet of the rotor so that the coil heads pass above and below the flatfront sides of this magnet and engage the pivot of the rotor into thebearing 34 at the same time as-the coil elements are put into place byengaging the bases 50 into the corresponding holes of the mountingplate. Once this operation has been accomplished the ring 51 can beplaced in the appropriate position after which the bridge 32 is put intoplace as in the case of a conventional bridge of mechanical movement byengaging the pivot 34 into the stone and the fixing bases 50 into theopenings provided for this purpose in the bridge 32. At that time thereis nothing further to do than to connect the extremities of the coils 48and 49 to the electronic device which provides distribution of thesurges and to place a pinion on the edge of the shaft 43. In thisoperation it could be useful to hold up the stone which forms thelowerbearing in order to prevent it from being driven out. One of theends of each coil is connected to a common connecting point so as toassure a connection in series of the two coils and the other end isconnected to the rest of the distributer.

In this form of design, since the bridge 32 can also carry the bearingsof at least part of the motor reduction unit which drives the hands, thedistance between axes of the first stage of this gear train isdetermined in production. This assures optimum efficiency. ln effect,the hole 39 which accepts the bearing of the motors rotor and the hole(not shown) which accepts the bearing of the second moving part of thisgear are cut out and honed over again simultaneously into the bridge 32so that the closest tolerance levels can be maintained. Since the holesfor the fixing bases 50 can be also honed during the same operation, itcan be seen that optimum precision is achieved in the positioning of thedifferent parts of the motor.

Another advantage of the design described is that the bearings of themotor are easily accessible and that the hopping about of the rotor canbe regulated by conventional means by adjusting the position of thestones 34 and 40. Regulation of the oil can also be done more easilyduring the course of the operation.

Lastly, the design described provides for minimum bulkiness,particularly a construction of the smallest possible height. In effect,the sides of the spirals of the windings pass immediately above thefront surfaces of the rotor.

Lastly, FIG. 7 shows a design variant of the winding support. Thiselement which replaces the coil elements 45 and 46 can also be obtainedby moulding or injection of plastic material, for example plexiglas, bycalcing or by machining in a metallic mass. It is composed of anon-magnetic material and presents the general shape of a cylindricalbody 61 into which are arranged two annular grooves 62 and 63 and anaxial piercing 64. Each one of the two grooves 62 and 63 extend alongtwo generatrices and two chords in in side surface and in the frontsurfaces of the element 61. They are symmetrical with respect to adiametrical plane. As regards the piercing, it is done coaxially to theelement 61 and has a diameter slightly greater than the diameter of therotor. This coil support permits a design which is a combination of thatof FIGS. 1 and 5. The rotor is engaged in the passage 64 prior toeffecting the winding. After that the spirals of the coils are woundinto the grooves 62 and 63, the rotor being held in place so that laterit is trapped between the two windings. The central webs 65 assure theguiding of the winding. The element 61, wound and provided with a sleevesimilar to the sleeve 51, is placed between the mounting plate and thebridge of the clockwork movement, the pivots of the shaft engaging inthe bearings which are carried by these two frame elements.

The seating 66 placed in the front surfaces of the element 61 are alsointended for accepting fixing pins and centering pins similar to thepins 50.

In this variation the coils can be completely immersed in the grooves 62and 63. It is therefore not necessary to provide in the mounting plateand in the bridge of the motor openings corresponding to the openings37, 38, 41, 42 of FIGS. 5 and 6 and the winding is housed entirelybetween the inside surfaces of the frame elements.

What is claimed is:

1. An electric motor for a watch comprising: a cylindrical rotordiametrically permanently magnetized; a non-magnetic coil support; twostator coils having flat turns parallel to the axis of said rotorcarried on said support member; wherein, in an area adjacent said rotor,said stator coils are supported on said support at their end portions,with central portions of said coils extending unsupported over theadjacent surfaces of said rotor.

2. A motor according to claim 1, wherein said coil support is formed oftwo bodies, each having a concave face in the shape of a cylindricalarc, each bearing at least a first portion of said stator coil andfastened opposite each other between said frame elements such that saidcentral portions of said coils at least partially enclose saidcylindrical rotor.

3. A motor. according to claim 2, wherein said coil bodies arepositioned between said frame elements by guide feet.

4. A motor according to claim 1, wherein said coil support comprises apart cylindrically shaped member having an axial bore therethrough andhaving in its cylindrical side face and its front faces two annulargrooves extending along planes parallel to the axis of said member.

5. An electric motor for a wrist watch, comprising: a cylindrical rotordiametrically permanently magnetized; a coil support member made of asingle piece of a non-magnetic material; a cylindrical passage extendingthrough said support member for lodging said rotor; a pair of annulargrooves provided in the outer side face and both front faces of saidsupport member, said grooves extending parallel to one another andsymmetrically with respect to the axis of said cylindrical passage andparallel to said axis; a pair of driving coils having flat turns andwound each in one of said grooves, said coils having front sides whichare supported only at their end portions by said support member, whereasthe central portion of each front side extends unsupported over theadjacent surface of said rotor.

6. An electric motor according to claim 5, further comprising: two frameelements fixedly connected to one another; a pair of bearings eachsecured to one of said frame elements; and a shaft which supports saidrotor; said support member being secured between said frame elements,and said shaft having two end portions each engaging one of saidbearings.

7. An electric motor according to claim 6, wherein said support memberside face is of cylindrical shape and wherein a cylindrical shieldmember of a ferromagnetic material of high permeability and lowremanence is provided, said shield member extending around said supportmember and said coils and being held in place by said frame elements.

8. A motor according to claim 7, wherein said frame elements comprisethe pillor plate and a bridge of said watch.

9. A motor according to claim 7, wherein said frame elements arefastened to each other, and said coil support is positioned betweenthese frame elements by guide feet.

10. An electric motor for a wrist watch, comprising: a cylindrical rotordiametrically permanently magnetized; a coil support comprising twoparts of a nonmagnetic material, each part having a concave inner sideface in the shape of a cylindrical arc and an annular groove provided inthe outer side and the front faces of each part, parallel to the axis ofsaid cylindrical face; a pair of driving coils having flat turns andwound each in one of said grooves, said coils having front sides whichextend each at one end of said concave faces and are supported at theirend portions by one of the support parts; a pair of frame elementsfixedly connected to one another; a pair of bearings each secured to oneof said frame elements; and a shaft which supports said rotor; both saidsupport parts being held by said frame elements in such positions thatsaid concave faces surround said rotor coaxially, and central portionsof each front side of the coils extend unsupported over an adjacentsurface of said rotor, said shaft having two end portions which eachengage one of said bearings.

11. An electric motor according to claim 10, further comprising acylindrical shield member of a ferromagnetic material of highpermeability and low remanence, lodged between said frame elements,surrounding both said support parts and said coils and held in place bysaid frame elements.

12. A motor according to claim 7, wherein one of the end portions ofsaid shaft projects through said bearing on the outer side of thecorresponding frame element, said projecting end portion being intendedto receive a pinion.

1. An electric motor for a watch comprising: a cylindrical rotordiametrically permanently magnetized; a non-magnetic coil support; twostator coils having flat turns parallel to the axis of said rotorcarried on said support member; wherein, in an area adjacent said rotor,said stator coils are supported on said support at their end portions,with central portions of said coils extending unsupported over theadjacent surfaces of said rotor.
 2. A motor according to claim 1,wherein said coil support is formed of two bodies, each having a concaveface in the shape of a cylindrical arc, each bearing at least a firstportion of said stator coil and fastened opposite each other betweensaid frame elements such that said central portions of said coils atleast partially enclose said cylindrical rotor.
 3. A motor according toclaim 2, wherein said coil bodies are positioned between said frameelements by guide feet.
 4. A motor according to claim 1, wherein saidcoil support comprises a part cylindrically shaped member having anaxial bore therethrough and having in its cylindrical side face and itsfront faces two annular grooves extending along planes parallel to theaxis of said member.
 5. An electric motor for a wrist watch, comprising:a cylindrical rotor diametrically permanently magnetized; a coil supportmember made of a single piece of a non-magnetic material; a cylindricalpassage extending through said support member for lodging said rotor; apair of annular grooves provided in the outer side face and both frontfaces of said support member, said grooves extending parallel to oneanother and symmetrically with respect to the axis of said cylindricalpassage and parallel to said axis; a pair of driving coils having flatturns and wound each in one of said grooves, said coils having frontsides which are supported only at their end portions by said supportmember, whereas the central portion of each front side extendsunsupported over the adjacent surface of sAid rotor.
 6. An electricmotor according to claim 5, further comprising: two frame elementsfixedly connected to one another; a pair of bearings each secured to oneof said frame elements; and a shaft which supports said rotor; saidsupport member being secured between said frame elements, and said shafthaving two end portions each engaging one of said bearings.
 7. Anelectric motor according to claim 6, wherein said support member sideface is of cylindrical shape and wherein a cylindrical shield member ofa ferromagnetic material of high permeability and low remanence isprovided, said shield member extending around said support member andsaid coils and being held in place by said frame elements.
 8. A motoraccording to claim 7, wherein said frame elements comprise the pillorplate and a bridge of said watch.
 9. A motor according to claim 7,wherein said frame elements are fastened to each other, and said coilsupport is positioned between these frame elements by guide feet.
 10. Anelectric motor for a wrist watch, comprising: a cylindrical rotordiametrically permanently magnetized; a coil support comprising twoparts of a non-magnetic material, each part having a concave inner sideface in the shape of a cylindrical arc and an annular groove provided inthe outer side and the front faces of each part, parallel to the axis ofsaid cylindrical face; a pair of driving coils having flat turns andwound each in one of said grooves, said coils having front sides whichextend each at one end of said concave faces and are supported at theirend portions by one of the support parts; a pair of frame elementsfixedly connected to one another; a pair of bearings each secured to oneof said frame elements; and a shaft which supports said rotor; both saidsupport parts being held by said frame elements in such positions thatsaid concave faces surround said rotor coaxially, and central portionsof each front side of the coils extend unsupported over an adjacentsurface of said rotor, said shaft having two end portions which eachengage one of said bearings.
 11. An electric motor according to claim10, further comprising a cylindrical shield member of a ferromagneticmaterial of high permeability and low remanence, lodged between saidframe elements, surrounding both said support parts and said coils andheld in place by said frame elements.
 12. A motor according to claim 7,wherein one of the end portions of said shaft projects through saidbearing on the outer side of the corresponding frame element, saidprojecting end portion being intended to receive a pinion.